1. Field of the Invention
The present invention relates to lead forming of a semiconductor device.
2. Description of Prior Art
A semiconductor device has leads extending through two sides of a resin package. In a fabrication process of semiconductor device, the leads are formed after the semiconductor device is covered with a resin. For example, when gull-wing type leads are formed in a prior art process, a semiconductor device, after being covered with a resin, is put between top and bottom dies for preliminary bending, so that lead parts extending from the two sides of the semiconductor device are bent in a press. Next, the semiconductor device is put between top and bottom dies, so that distal portions of the lead parts are bent in the reverse direction in a press. Then, the semiconductor device having the gull-wing leads is put between top and bottom dies for adjustment, to produce a final form.
In the above-mentioned lead forming, when the type of semiconductor device is changed or even if the type is not changed, but the shape of the leads is changed, all of the three die assemblies have to be replaced. That is, the dies are needed for each lead shape of semiconductor device. Therefore, much capital investment, labor and time are needed.
In the above-mentioned lead forming, exclusive die assemblies each consisting of top and bottom dies are necessary according to a size of a work to be formed. Therefore, it is proposed to use a general die. For example, in the die disclosed in Japanese Utility Model laid open Publication 60-99033/1985 for bending a work such as a wire or a plate with press work, the position of a top die in a die assembly can be changed vertically. Furthermore, one of die assemblies provided at right and left sides can be moved horizontally with a screw. It is to be noted that lead forming of a semiconductor device is not described. Further, in an apparatus for bending disclosed in Japanese Patent laid open Publication 6-47445/1994, a die consists of a plurality of components, and one of them is movable. The shape of the die can be changed by moving the movable component. It is to be noted that the publication also does not describe lead forming of a semiconductor device. An apparatus for lead bending, disclosed in Japanese Patent laid open Publication 10-163396/1998, has a holder for holding the leads at bases thereof and another holder for holding them at edges thereof. When the bending form of lead is changed, the positions at the base and/or at the edge have to be changed. Then, the positions of the holders are adjusted, and the edges of the leads are moved like an arc so as to form the leads.
Furthermore, in the apparatuses disclosed in Japanese Utility Model laid open Publication 60-99033/1985 and Japanese Patent laid open Publications 6-99033/1994 and 10-163396/1998, the position or the like of a die can be changed according to a work to be processed. However, they cannot realize high precision of the order of for example one micrometer. For example, in the apparatuses shown in Japanese Utility Model laid open Publication 60-99033/1985 and Japanese Patent laid open Publications 6-99033/1994 do not form leads, and they do not take high precision into account, for example, by adjusting the die position with a screw. Furthermore, in the apparatus for lead bending shown in Japanese Patent laid open Publication 10-163396/1998, the die assembly for lead bending does not have a punch and a die. In the apparatus the lead portions are clamped at a base position and at a forming position, to enforce an arc trajectory so as to form the lead parts. However, such forming has low precision consequently. Further, these apparatuses only bent the lead portions, and they cannot deal with a complicated form of leads.